Roller furling and roller reefing (partial furling) of sails has come to be common and popular on a substantial variety of sailing vessels, and permits effective sail handling with reduced crew requirements and a host of other advantages.
In such systems, the sail is supported on and fixed to a stay which is adapted to rotate. When the sail is in place, it will be furled by being rolled around the outside of the rotatable stay. When fully rolled up, or furled, the sail may be left in place, ready for immediate use, not requiring stowage below decks, or crew handling to get it there. Unfurling is rapid and undemanding, so that making sail and getting under weigh is facilitated.
A wide variety of roller furling systems are known in the art, and do not per se form a part of the present invention, which is suitable for use with any such system.
Roller furling systems are also frequently employed in partially furled condition to reef the sail. In increased winds, where the sail area is greater than desirable, roller reefing is effective to reduce sail area, heeling moment, leeway, and to preserve control, particularly steering control, of the vessel. Roller reefing is progressive, and adaptable to wind and wave conditions as they occur. The alternative to reefing is to change to a smaller sail, which is demanding of crew and in some conditions working on the bow is hazardous. Other reefing techniques for headsails are not generally desirable, and represent little or no improvement on changing sails.
It is characteristic of such roller furling systems that as the luff of the sail is rolled on its stay, luff tension on the sail is decreased, and to a degree the bulk of material in the structure of the foot and leach of the sail cause the volume of material rolled around the stay to be greatest at the tack and the head. As a consequence, the sail develops excessive sag and draft in the center, and the location of the maximum draft moves aft. The problem is exacerbated by bias stretch of the sail fabric, which is ordinarily least controllable in the central portions of the sail structure. These aspects of roller furling are counter productive, as the shape of the sail is less effective, particularly for sailing to windward. Heeling moments remain higher than desirable, and boat performance is lost.
It has long been recognized that increasing the bulk of the roll in the mid-region of the luff of the sail as it is partially furled can alleviate much of the problem, and make roller reefing a far more effective technique. It is also known that the increased bulk of the furled sail on the stay is aerodynamically superior to the sag and stretch of the sail.
Such expedients as enlarging the central, mid-luff portion of the stay, or hoisting an elongated member along the luff to become rolled into the sail as the furling takes place have been tried. The enlarged stay is aerodynamically undesirable. The hoisting of a luff "partner" is a backward step, since it puts the crew back on the bow of the vessel in dangerous conditions and circumstances.